1. Field of Invention
This invention relates to novel anticancer agents having potent antineoplastic activity without systemic toxicity or mutagenicity. Moreover, the compounds of the present invention present higher specificity to cancer cell targets than previously known compounds. The present invention also relates to pharmaceutical compositions comprising at least one compound of the present invention as active agent. More specifically, the invention is directed to novel derivatives of 1-aryl-3-(2-chloroalkanyl)ureas having substituents on the first carbon atom of the 2-chloroalkanyl moeity.
2. The Prior Art
Some 1-aryl-3-(2-chloroalkanyl)urea derivatives (hereinafter referred to as xe2x80x9cCAUsxe2x80x9d) are known from U.S. Pat. Nos. 5,530,026 and 5,750,547 to the same assignee as the present application. More specifically, compounds of the following formula are known: 
wherein R refers to various substituents on the phenyl ring.
It is known that CAUs display an affinity towards cancer cells, permeate the cell wall and provide a mild alkylating effect on cell components thereby killing the offending cell.
An object of the invention is to provide novel CAU derivatives having significantly superior antineoplastic activity over known CAUs while maintaining low systemic toxicity, mutagenicity and side-effects.
It has now been found, against expectations and documented precedents that specific substitutions on the first carbon atom of the 2-chloroalkanyl group of the CAU molecule provides a significant improvement on the anticancer effect of the resulting CAU.
Moreover, it has been found that yet unknown substitutions on the phenyl ring render the resulting CAU molecule even more efficient at targeting specific regions of cancerous cells thereby improving their specificity toward various cellular proteins key to cell survival.
More specifically, this invention provides a novel class of CAU derivatives. This novel class of CAU may be expressed by the following formula: 
wherein
R1 is H, C1-C6 alkyl, C3-C7 cycloalkyl, C1-C6 alkoxy, C1-C6 hydroxy alkyl, C1-C6 halide C1-C6 halo substituted C1-C6 alkyl, halo di-substituted C1-C6 alkyl or halo tri-substituted C1-C6 alkyl;
R2 is C1-C6 alkyl, C3-C7 cycloalkyl, C1-C6 alkoxy, C1-C6 hydroxy alkyl, C1-C6 halide, C1-C6 halo substituted C1-C6 alkyl, halo di-substituted C1-C6 alkyl or halo tri-substituted C1-C6 alkyl;
R1 and R2 could also be part of cyclic structures expressed by the formula: examples: 
R3 and R4 are as defined in R6, or halide, dihalide or trihalide (e.g. CF3) lower dialkyl (1 to 8 carbon atoms)
in R3 and R4, (the number of carbon atoms present is not necessarily identical (xe2x80x9casymetric moleculesxe2x80x9d), or
alicyclic groups of the following structures 
wherein n=1 to 3 carbon atoms,
The alicyclic ring could also be substituted by one or more substituting groups comprising groups as described for R6 
R3 and R4 can also be polycyclic rings bearing not more than three rings such as dihydrophenanthrene, anthracene, phenanthrene, fluorenyl, etc., examples: 
wherein the rings other than the ring bearing the substituted 2-chloroethylamino moiety can be substituted by one or more groups as defined in R6.
R5 is H
and R6 
lower alkyl (1 to 7 carbon atoms) or
lower alkoxy or hydroxy alkyl, amino alkyl, thio alkyl (1 to 7 carbon atoms) or
S-lower alkyl
N-lower alkyl
N,N-dilower alkyl
lower cyanoalkyl (1 to 7 carbon atoms)
cycloalkyl (3 to 7 carbons atoms)
lower haloalkyls (Br, I, Cl, F) (1 to 7 carbon atoms)
lower sulfoxides (1 to 7 carbon atoms)
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. It should be understood, however, that this detailed description, while indicating preferred embodiments of the invention, is given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art.
Before describing the present invention in detail, it is to be understood that the invention is not limited in its application to the details of the preferred embodiments and examples described herein. The invention is capable of other embodiments and of being practised in various ways. It is also to be understood that the phraseology or terminology used herein is for the purpose of description and not limitation.
Experiments to assess the biopharmaceutical properties of known 1-aryl-3-(2-chloroethyl) ureas (CAUs) have unexpectedly revealed that certain cell enzymes such as cytochromes P450 1A2 and 2E1 were oxidizing CAUs therefore metabolizing them to inert molecules and depriving them of anticancer effect. The metabolization mechanism was again unexpectedly found to operate on the first carbon atom on the chloro-2-alkenyl moiety adjacent to the urea moiety. 
For example, in the case of a 4-tert-butyl CAU (tBCAU), metabolization occurred along the following pathway: 
Surprisingly this has revealed a metabolic weak spot at the first carbon atom of the 2-chloro-alkanyl moiety of the CAUs. Thus, the present invention generally aims at providing protecting groups on this first carbon atom and at providing novel CAU derivatives having potent antineoplastic activity.
More specifically, the protection of the weak carbon atom from metabolization was achieved by substituting the hydrogen atoms with groups such as lower alkyl groups such as methyl, ethyl and propyl.
Furthermore, it was surprisingly discovered that certain modifications of substituents on the aryl moiety dramatically improved the specificity of the resulting CAU derivatives toward various cellular proteins key to cell survival.
Thus, the following compounds were developed and are expressed by the general formula: 
Wherein
R1 is H, C1-C6 alkyl, C3-C7 cycloalkyl, C1-C6 alkoxy, C1-C6 hydroxy alkyl, C1-C6 halide C1-C6 halo substituted C1-C6 alkyl, halo di-substituted C1-C6 alkyl or halo tri-substituted C1-C6 alkyl;
R2 is C1-C6 alkyl, C3-C7 cycloalkyl, C1-C6 alkoxy, C1-C6 hydroxy alkyl C1-C6 halide, C1-C6 halo substituted C1-C6 alkyl, halo di-substituted C1-C6 alkyl or halo tri-substituted C1-C6 alkyl;
R1 and R2 can be part of cyclic structures expressed by the formula: 
wherein n=1 to 6, such as: 
wherein the arrows on the molecule on the right hand side indicate the position where the molecule can be substituted by the chlorine atom;
R3 and R4 are as defined in R5 or halide, dihalide or trihalide (e.g. CF3) lower dialkyl (1 to 8 carbon atoms)
in R3 and R4, (the number of carbon atoms present is not necessarily identical (xe2x80x9casymetric moleculesxe2x80x9d) or
alicyclic groups of the following structures 
wherein n=1 to 3 carbon atoms (R5 is shown to clearly convey that the fused alicyclic group is fused at the 3 and 4 positions on the phenyl ring,
R3 and R4 can also be polycyclic ring systems bearing not more than three rings such as dihydrophenanthrene, dihydroanthracene, anthracene, phenanthrene, fluorenyl, etc., examples: 
wherein the rings other than the ring bearing the substituted 2-chloroethylamino moiety can be substituted by one or more groups as defined in R6.
R5 is H
R6 lower alkyl (1 to 7 carbon atoms) or
lower alkoxy or hydroxy alkyl amino alkyl, thio alkyl (1 to 7 carbon atoms) or
S-lower alkyl
N-lower alkyl
N,N-dilower alkyl
lower cyanoalkyl (1 to 7 carbon atoms)
cycloalkyl (3 to 7 carbons atoms)
lower haloalkyls (Br, I, Cl, F) (1 to 7 carbon atoms)
lower sulfoxides (1 to 7 carbon atoms)
The compounds of the present invention are easily prepared in good yields without concomitant polymerization or decomposition. The compounds are also easily purified by usual techniques such as crystallization or liquid chromatography. Furthermore, the compounds exhibit an extended shelf life without decomposition in air.
The type and level of activity for a given dosage of each compound can be conventionally determined by routine experimentation using well-known pharmacological protocols.
The compounds of the present invention appear to kill cancer tumor cells by alkylation of their xcex2-tubulin on a specific cysteine residue (Cyst-239) and also by other mechanisms under investigation. The molecular structure of xcex2-tubulin has been highly conserved throughout evolution and is therefore present many mammalian cells. Consequently, the compounds of the invention are indicated for: wideranging anticancer agents, transdermic for pre-surgical treatment of melanomas and systemic for other cancers.
Prodrugs of the compounds of the present invention may also be easily prepared. As an example of prodrugs of the compounds of the present invention, the sulfone and sulfoxide derivatives of alkylthio substituents is immediately contemplated by skilled worker in this art. The sulfone and sulfoxide derivatives while not generally active will be activated once administered to a patient. The activation will occur when the prodrug is reduced to yield the corresponding alkylthio, an active compound.
The following synthesis flowsheet illustrates one route of preparation of CAU derivatives of the present invention. 
It is important to note that the preparation of CAU derivatives of the present invention has led to the formation of R and S isomers which (in some cases) exhibit significant differences in cytotoxic activities (see Tables I and II below).